1. Field of the Invention
This invention relates to copolymers of maleic anhydride and a C.sub.1 -C.sub.4 alkyl vinyl ether, and, more particularly, to a general process for making such copolymers of predetermined specific viscosity.
2. Description of the Prior Art
Commercial processes are available for making copolymers of maleic anhydride and a C.sub.1 -C.sub.4 alkyl vinyl ether. However, it has been found necessary to provide a different process for a copolymer of low specific viscosity, or molecular weight, than for a copolymer of medium range viscosity, and still another process for a copolymer of relatively high specific viscosity.
In these several processes, the molecular weight of the copolymer can be controlled either by adjusting the temperature of the polymerization, the concentration of the polymerization initiator and/or the kind of solvent utilized for the polymerization. Usually, higher polymerization temperatures will produce lower molecular weight copolymers, while higher concentrations of the polymerization initiator will produce lower molecular weight copolymers. The effect of the solvent used is to combine with the free radicals produced by the initiator to terminate the reaction at a point at which the weight copolymers. The effect of the solvent used is to combine with the free radicals produced by the initiator to terminate the reaction at a point at which the polymerization had progressed on a particular chain. This degree of interference with the polymerization on the part of the solvent can be determined from its chain transfer constant. Solvents having a low chain transfer constant, such as benzene, exhibit only a relatively slight tendency to interfere with chain-reaction type polymerizations; while solvents with a relatively high chain transfer constant, such as xylene, exert a rather high degree of interference with such polymerizations. Accordingly, for processes defined by a given polymerization temperature and initiator level, a low chain transfer constant solvent generally will produce higher viscosity (higher molecular weight) copolymers while higher constant solvents will provide lower viscosity (lower molecular weight) copolymers.
Accordingly, it is an object of this invention to provide a general process applicable for making copolymers of maleic anhydride and a C.sub.1 -C.sub.4 alkyl vinyl ether having a predetermined specific viscosity extending a wide viscosity range.
A particular object of this invention is to provide a general process using a solvent having a high chain transfer constant, whose addition at different times during the polymerization can predetermine the specific viscosity of the copolymers produced.
These and other objects and features of the invention will be made apparent from the following description of the invention.